This invention relates to turbines and other such devices capable of interacting with a flow of fluid in such a manner as to transfer energy from the fluid to a mechanical device. This invention relates more particularly to turbines or other such devices arranged to be driven by the action of a flow of water or other liquid medium. Thus, the present invention relates in particular to the use of turbines and similar moving devices for extracting kinetic energy from flowing water for the purposes of utilising such kinetic energy to produce either electricity or shaft power for utilisation for a required purpose. Flowing water (which may be either fresh water or sea water) used in the context of this invention is a characteristic of tidal, marine, estuarial or river currents.
It is known how to use turbines for such purposes. For example, in our British Patents GB 2256011 B, GB 2311566 B and No 2348250 we have disclosed constructions pertaining to water driveable turbines; i.e. rotors supported within the water column of the sea, river or an estuary so that the flow of water may turn the rotor to produce shaft power and hence possibly electricity for utilisation for a required purpose.
In particular the present invention relates to a power transmission system for use with one or more such turbine rotors for extracting kinetic energy from flowing water and producing therefrom electricity by driving an electrical generator or alternator or for applying the power for some other useful purpose requiring a fast rotating shaft.
Generally a turbine for extracting kinetic energy from water currents, whether in a river or at sea, includes a rotor capable of interacting with the flow of water in such a way that some of the energy of motion of the passing mass of water causes the rotor to rotate. No matter what kind of rotor is used, whether an axial flow or propeller type of rotor or a cross-flow rotor of the so-called Darrieus type, or even some other form of hydrofoil device reacting against the flow of water currents, the rotation of a rotor driven by the movement of water currents will be slow due to the fact that even the fastest of water currents only run at relatively slow speeds in the range from 2 to 4 m/s at most and the rotor extremities cannot generally move much faster than 10 to 15 m/s. Consequently only small devices can rotate at reasonably high speeds since the larger the device i.e., diameter of the rotor, generally the smaller the angular movement in a given time.
Therefore, it becomes necessary to provide some means for speeding up the output gained from the rotation of a slow moving rotor in order to effectively drive an electrical generator or other relatively high speed machinery. For example an axial flow tidal or river current turbine rotor 15 m in diameter will typically rotate at about 10 revolutions per minute in a driving water current of 2 to 2.5 m/s (4 to 5 knots) but most conventional electricity generators typically require to be driven at shaft speeds of 1000, 1500 or more revolutions per minute. This situation indicates that there is therefore a need to increase the speed of the main turbine shaft by a factor of 100 or, more. The most generally proposed technique, which is prior art, is by using a multistage gearbox. However gearboxes of such a kind are complicated mechanically, heavy to handle, costly, suffer significant wear and require regular maintenance to replace the lubricant conventionally provided between relatively moving components of the turbines. Furthermore, gearboxes conventionally involved also introduce a hazard to the local environment should the lubricating oil leak out for any reason.